Or at least that's what Joystiq's Rowan Kaiser believes and attempts to explain in his latest RPG-focused editorial. And given my absolute admiration for Crusaders of the Dark Savant, you won't hear any complaints out of me when someone praises one of its many virtues:
Characters in-game have the ability to change classes. This can make them extremely powerful in a few respects. First of all, a character in a new class requires the same amount of experience to level up as a new character. At roughly level 10, the amount of experience points required to achieve level 11 is about the same as the amount required from levels 1-10. Characters also keep their existing skills, spells, and hit points, which both continue increasing with further levels, instead of stagnating (as in AD&D dual-classing). They can also continue developing skills from their previous classes.
For example, certain classes like Ninjas, Thieves, and Bards can all use the "Ninjitsu" skill, which allows them to hide during combat. If they've developed this skill at all during their time in that class, in the new class, they'll still be able to hide and add points to Ninjitsu when they level up, even if they switch a class that doesn't have Ninjitsu. So you can have a heavily armored, well-hidden, backstabbing Valkyrie.
How do you improve statistics to switch classes? When characters level up, the game randomly picks statistics to improve by a single point. The number of stats which are improved are random, as are the statistics themselves. You cannot influence this directly, unlike the bonus roll.
The Dwarf Fighter in the image above progressed several levels, and the amount of experience needed for him to progress has dramatically increased. He's also done very well in terms of getting bonuses for his base statistics. His intelligence is a little low, so he doesn't have many options for changing class, but you only need one in this case, the Monk. So he switches (below).